In this study, an analysis is performed for the first time on the relationship between the levels of SF inflammatory factors and the patient's functional scores and the severity of OA in imaging examinations after electroacupuncture intervention, with the results demonstrating that the levels of SF inflammatory factors decrease significantly. By further correlation analysis, more significantly, the level of IL-6 in SF is significantly correlated with the function and pain (VAS, WOMAC and Lysholm scores) of patients with KOA. Besides, there is a significant correlation between IL-6, MMP-1 and the severity of OA in imaging examinations (K-L grade), which indicates that IL-6 and MMP-1 may be relatively suitable biomarkers for the diagnosis of OA. Meanwhile, it is demonstrated in this study that compared with the control group, the EA group has better functional recovery and better pain relief, which is a safe and effective method in the treatment of OA.
It is reported that many factors in interleukins (ILs) and matrix metalloproteinase family (MMPs) have great potential to be inflammatory biomarkers for the diagnosis of OA and the judgment of the severity of OA [26]. IL-6 and IL-8, as pro-inflammatory cytokines in ILs, can act as an effective chemokine and play a role in OA. Beekhuizen et al. [27] draw a comparison on the levels of 47 cytokines in OA patients and healthy individuals, and find that IL-6 increases significantly in OA patients. Similarly, Livshits et al. [28] find that IL-6 has a significant correlation with K-L classification, which can be employed as an important predictor of the severity of KOA. Kaneko S [29] finds that the levels of IL-6 and IL-8 in SF and serum negatively correlate with the progression of OA after a comparison of them. However, there are also some contradictory conclusions in some studies. Ding J et al. [30] draw a comparison on the levels of synovial fluid biomarkers in patients with KOA and meniscus injury (MI). Although they find that the levels of IL-6 and IL-8 in patients with OA do increase, there is no significant correlation between their levels and the severity of OA. As per a study of Brenner, there is no correlation between IL-6 levels and WOMAC scores [31]. It has also been reported by Leung YY [32] that there is no correlation between IL-8 levels and pain. As for this contradictory phenomenon, we consider that it may be caused by the bias of patients' general data when patients are included during the study design, such as ethnic differences and small sample size. More importantly, after consulting the literature we found that 85% of the studies on SF correlation in OA in recent years are cross-sectional studies [33], and there is no analysis of the correlation between the levels of SF inflammatory factors and the severity of OA and function scores during electroacupuncture treatment. Therefore, a longitudinal study with a follow-up time of 6 months is designed. In this study, the correlation analysis is adopted for the first time to evaluate the correlation between the levels of SF inflammatory factors and the severity of OA and functional scores, with the results showing that IL-6 levels and VAS scores (r = 0.45, p < 0.001) are positively correlated with WOMAC score (r = 0.3, p < 0.001), while are negatively correlated with K-L classification (r=-0.54, p < 0.001) and Lysholm scores (r=-0.27, p < 0.001). IL-8 is positively correlated with VAS scores (r = 0.32, p < 0.001), while negatively correlated with Lysholm scores (r=-0.19, p = 0.0027). IL-8 did not correlate significantly with K-L classification and WOMAC scores. These results indicate that the level of IL-6 is correlated with inflammatory pain and functional impairment of patients with OA and the severity of OA in imaging examinations.
In addition to ILs, MMPs, as an inflammatory factor, are secreted by chondrocytes, synovial fluid and synovial cells, and they can promote the decomposition of extracellular matrix (ECM), which would induce the possible destruction of the basic structure of cartilage, thus becoming a load that makes cartilage unable to support joints and then causing pain. MMP-1 is an interstitial collagenase generated in chondrocytes, osteoblasts and synoviocytes, and leads to type 1, type 2 and type 3 fiber decomposition and cartilage destruction in ECM, which would promote the development of OA [34]. MMP-3 is a matrix degrading enzyme with the specificity of promoting the degradation of such extracellular matrix proteoglycans as aggrecan, and it can also promote the development of OA by changing ECM [12]. Currently, there are many studies on the correlation between MMP and OA. Hwang IY et al. [35] find that the concentration of MMP-1 is very high in the early-stage OA and would decrease with the progression of this disease, which indicates that MMP-1 plays an important role in the early stages of OA, and their function would decrease with the progression of this disease. Heard BJ et al. [12] draw a comparison on the SF levels of healthy individuals and patients with KOA and rheumatoid arthritis (ROA). As per the principal component analysis (PCA), they find that the expression levels of MMP-1 and MMP-3 would be higher in the advanced stage of OA, which shows a positive correlation between them. However, Anitua E et al. [36] find that MMP-1 and MMP-3 do not correlate with the severity of OA when PCA is employed to analyze four biomarkers of OA. In a study by Schmidt-Rohlfing B [37] et al. involving 73 OA patients, it is also found that the levels of MMP-1 and MMP-3 do not correlate with the severity of OA. These contradictory research results suggest that it is necessary to conduct more studies to confirm the level changes of MMP in OA. In this study, an exploration is performed on the correlation between MMP-1, MMP-3, functional scores and the severity of OA, with the results showing that the level of MMP-1 does not significantly correlate with VAS, WOMAC and Lysholm scores. However, it negatively correlates with K-L classification (r=-0.29, p < 0.001), which is consistent with the findings of Hwang IY et al. [35], thus indicating that the level of MMP-1 is lower in the advanced stages of OA. Due to the fact that MMP-1 is secreted by chondrocytes, a decrease in secretion level may be caused by severe cartilage destruction in the advanced stages of OA. In addition, the level of MMP-3 is lower than that of the control group in the follow-up at the sixth week and the sixth month in this study (p < 0.05). As per correlation analysis, it is found that the level of MMP-3 is only positively correlated with WOMAC scores (r = 0.48, p < 0.001). It is the first time that this correlation is observed in patients with OA after electroacupuncture, which indicates that MMP-1 and MMP-3 may not be suitable for evaluating the functional rehabilitation of OA, while MMP-3 can reflect the severity of OA and is expected to be employed as a biomarker for determining the procession of OA.
EA has been used for managing variety of pain conditions [38]. It has been demonstrated in many studies that acupuncture is effective in the treatment of OA. As per the Nonpharmacologic and Pharmacologic Therapies in OA [19] issued by American College of Rheumatology, acupuncture therapy can be the first choice when pharmacologic therapies are not effective. Vickers et al. [39] propose in a meta-analysis involving 39 studies with a total of more than 20,000 patients that acupuncture is effective in relieving pain of patients with OA in clinical practice and can improve joint function. Zhou T et al. [40] perform the electroacupuncture on 40 patients with KOA (course of disease 17.2 ± 2.2 months), and they find that the VAS score of patients decreases, the Lysholm score increases, and the pain is relieved and the function is improved significantly. However, there is still controversy over the effect of electroacupuncture. As per the Evidence-Based Clinical Practice Guideline on Surgical Management of Osteoarthritis of the Knee [19] issued by American Academy of Orthopaedic Surgeons in 2015, acupuncture is objected in the treatment of OA and is considered to be ineffective. Hinman [41] research team adopts acupuncture to treat OA patients over 50 years old, and they find that acupuncture cannot improve WOMAC scores of OA patients over 50 years old. Therefore, the differences recommended by the guidelines and the contradictions in clinical research results suggest that it is necessary to perform more clinical research to provide evidence-based medical evidence to support the effectiveness of acupuncture. In this study, VAS score and WOMAC score of OA patients in the electroacupuncture group after treatment are significantly lower than those before treatment (p < 0.05); VAS score is significantly lower in the follow-up at the sixth week and the sixth month compared with the control group (p < 0.05); WOMAC score is significantly lower in the follow-up at the sixth month compared with the control group (p < 0.05). In the electroacupuncture group, Lysholm score after treatment is significantly higher than that before treatment (p < 0.05), and significantly higher in the follow-up at the sixth week and the sixth month compared with the control group (p < 0.05). The above results indicate that electroacupuncture can achieve significant effects from both pain relief and function improvement, and electroacupuncture is an effective non-surgical treatment for OA. Thus, these results suggest that electroacupuncture had a clinically meaningful benefit in improving symptoms and relieving pain in patients with OA.
Previous studies showed the positive effects of EA in eliminating inflammation. Wu et al. [42] find that the levels of IL-1b and IL-6 in SF and cartilage in the EA treatment group are significantly reduced by a study on the OA rat model. Xu Y et al. [43] find that acupuncture could inhibit the expression of such inflammatory factors as TNF-α and IL-8 in the rat OA model. Besides, they find that acupuncture could exert a positive impact on relieving the inflammatory reaction of OA. These results suggest that EA is closely related to inflammatory factors. In addition, similar results have been obtained in a very small number of clinical studies via the analysis of the serum of patients with OA. Shi GX et al. [14] adopt electroacupuncture in the treatment of patients with OA, with the acupuncture group as the control group. After 8 weeks of treatment, it is found that the function and pain of patients are improved and relieved respectively, and the levels of various inflammatory factors (MMP-1, IL-18, MMP-13, etc.) in serum are significantly reduced, with a more obvious reduction of inflammatory factors in the electroacupuncture group. It has been preliminarily demonstrated in these studies that EA can effectively relieve the symptoms of OA by reducing inflammatory factors, but the results are relatively unreliable, due to the fact that SF specimens of patients in clinical practice are not collected for research. The biomarkers of serum and urine are easily affected by the whole- body system, which will hinder the identification of local changes. However, the biomarkers for measuring SF of knee joint can provide more information about the condition of affected joints and can directly reflect the changes in the internal environment of affected limbs. Besides, the concentration of biomarkers in SF is higher than that in blood or urine, and hence it has higher sensitivity and specificity [44]. Currently, there is no clinical study to analyze the level of SF inflammatory factors in the treatment process of OA with electroacupuncture. In this study, SF of patients after EA treatment is selected for analysis for the first time, multiple follow-up time points are determined, and the levels of inflammatory factors in SF are measured during the electroacupuncture treatment. As per the results, the levels of inflammatory factors in both groups could decrease after treatment. Compared with the control group, the levels of SF IL-6, IL-8 and MMP-3 in the follow-up at the sixth week and the sixth month are significantly lower than those in the control group (P < 0.05). In the follow-up at the sixth month, the level of MMP-1 in the electroacupuncture group is significantly reduced, which shows a statistical significance between both groups (P < 0.05). In this study, the results are consistent with those of the previous results. Besides, SF is selected for more specific and sensitive analysis in this study. Most importantly, clinical data of patients with OA are employed in the research and analysis, which further clarifies that electroacupuncture can improve the function and relieve pain of patients with OA by reducing ILs and MMPs.
Our research has several limitations. First, as a single-center study, the number of patients is small which resulting in limited statistical power, but the data collected from the patients in this study were complete and authentic. The clear and encouraging results in this study need more multicenter or longitudinal studies to validate. Second, this is a retrospective study, but our results were obtained through a comprehensive retrospective analysis of the data collected over a long period of time. Although we used strict inclusion and exclusion criteria during our study and used propensity matching analysis to eliminate bias, more prospective studies are needed.